This invention relates to the production of heavy petroleum from tar sands and the like and more particularly to an improved combustion air injection well design.
A method of producing petroleum from tar sands is described in U.S. Pat. No. 3,504,745, issued to Elkins and assigned to the assignee of the present invention. Basically, the method described involves a process of injecting air into the tar sand and initiating combustion to burn part of the tar and generate sufficient heat to reduce the viscosity of the remaining tar so that it may flow and be produced through a well. The patent also discloses some of the problems encountered in such operations and in particular the fact that the injected air tends to travel upward around the injection air wellbore. A solution to this problem taught by the patent is the injection of a foam-forming solution into the earth above the air injection point. This was accomplished by means of a small pipe or tubing which was placed into the well next to the normal casing and cemented into place with it. The small pipe ended above the air injection zone and was used to inject the soap solution which would then form a foam if air tried to pass through it and thereby block the air flow paths. This arrangement did not provide the desired blockage in all cases. This could be due to the fact that the soap solution was injected on only one side of the casing so that some vertical fractures on the opposite side may not have received the soap solution. It is also possible that the completion with two separate strings of pipe in the hole may prevent effective cementing due to the nonsymmetrical annulus and the creation of a trapped mud zone between the two pipe strings in the hole. In any case, it has been found that this type of completion does not always provide the desired vertical air blockage.
Accordingly, an object of the present invention is to provide an improved combustion air injection well completion.
Another object of the present invention is to provide an injection well completion providing means for uniformly injecting divertent fluid in all directions about the wellbore.
Another object of the present invention is to provide a combustion injection well having means for injecting a cooling fluid to protect the entire casing string from uncontrolled combustion zones above a divertent fluid injection depth.
Yet another object of the present invention is to provide a combustion air injection well completion which provides a uniform cementing annulus.
According to the present invention, the combustion air injection well is completed by means of an outer string having a large diameter upper portion and a smaller diameter lower portion connected together by a short swage and a small diameter liner casing positioned within the large diameter portion of the outer casing. The inner casing is screwed into the upper end of the small diameter portion of the outer casing. The outer casing is positioned in a wellbore such that the swage is located above a desired air injection level but below a desired divertent fluid injection level. The annulus between the inner and outer casings provides a conduit for injection of divertent or cooling fluid while the inner casing is used for injection of combustion air.